The Moon goes through 8 lunar phases in its 29.53 days lunar cycle. These phases are determined by the changing angles between the Sun, Moon, and Earth as the Moon orbits our planet and Earth orbits the Sun. As a result, the amount of sunlight that reflects off the Moon and reaches our eyes varies daily.
Astronomers have divided this cycle into four primary Moon phases: New Moon, First Quarter, Full Moon, and Last Quarter. Between these major phases, there are four minor ones: the Waxing Crescent, Waxing Gibbous, Waning Gibbous, and Waning Crescent.
Let's explore the different moon phases that can occur on March 31.
Waxing Crescent Phase
What Is The Waxing Crescent Moon? - Astronomy Made Simple
On this day, the Moon might be in a Waxing Crescent Phase. This is the first phase after the New Moon and is a great time to see the features of the moon's surface. The Waxing Crescent is best seen in the west after the sun dips below the horizon at sunset.
During this phase, the moon is close to the sun in the sky and mostly dark except for the right edge of the moon which becomes brighter as the days get closer to the next phase which is a First Quarter with a 50% illumination.
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The lit area slowly widens each day, covering more and more of the right side of the Moon’s surface until the first quarter phase, when the Moon’s entire right side is illuminated. (In the Southern Hemisphere, the same thing happens, only on the left side.)
Lunar phases.
The Waxing Crescent on March 31 can have a varying illumination. For example, one year it might have an illumination of 6%. This is the percentage of the Moon illuminated by the Sun. The illumination is constantly changing and can vary up to 10% a day.
Also, on March 31 the Moon can be 2.24 days old. This refers to how many days it has been since the last New Moon.
Moon Phases Calendar.
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Waxing Gibbous Phase
On March 31, the Moon will be in a Waxing Gibbous phase. Visible through most of the night sky setting a few hours before sunrise. This phase is when the moon is more than 50% illuminated but not yet a Full Moon.
During a Waxing Gibbous the moon rises in the east in mid-afternoon and is high in the eastern sky at sunset. The phase lasts about 7 days with the moon becoming more illuminated each day until the Full Moon.
The word Gibbous first appeared in the 14th century and has its roots in the Latin word "gibbosus" meaning humpbacked.
The Waxing Gibbous on March 31 can have a varying illumination. For example, one year it might have an illumination of 97%. The illumination is constantly changing and can vary up to 10% a day.
Also, on March 31 the Moon can be 13.11 days old. This refers to how many days it has been since the last New Moon.
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Waning Gibbous
On this day the Moon was in a Waning Gibbous. During this phase the Moon can be seen in the early morning daylight hours on the western horizon. This is the first phase after the Full Moon occurs.
It lasts roughly 7 days with the Moon’s illumination growing smaller each day until the Moon becomes a Last Quarter Moon with an illumination of 50%. The average Moon rise for this phase is between 9pm and Midnight depending on the age of the phase.
The moon rises later and later each night setting after sunrise in the morning.
The Waning Gibbous on March 31 has an illumination of 68%. The illumination is constantly changing and can vary up to 10% a day.
On March 31 the Moon is 20.39 days old. This refers to how many days it has been since the last New Moon.
Understanding Moon's Age
The term "Moon's age" refers to how many days it's been since the last new Moon, not the Moon's actual age. The span of time between one new Moon and the next is called a lunar cycle, lunation, lunar month, or synodic month and on average lasts for 29.53059 days. This translates to 29 days, 12 hours, 44 minutes, and 3 seconds.
The length of a lunar cycle can vary by more than 13 hours due to a few factors. For example, when the new Moon phase occurs at about the same the time as perigee (the point in the Moon’s elliptical orbit that is closest to Earth), shorter lunations result. When the new Moon phase occurs at about the same time as apogee (when the Moon is farthest from Earth), longer lunations result.
Percent Illumination
Percent illumination, listed in the Moon Phase Calendar under the Moon symbol, tells us how much of the Moon’s disk is lit, as seen from Earth. Looking at the calendar on this page, you can see that from new to full, the percentage increases, indicating the waxing stages, and from full to new, the percentage decreases, indicating the waning stages.
The New Moon is 0 percent illuminated (or totally dark); the First Quarter is essentially 50 percent illuminated (half of the disk is lit); the Full Moon is 100 percent illuminated (the entire disk is lit); and the Last Quarter is back to essentially 50 percent illuminated (half of the disk is lit).
We say “essentially” for the quarter phases because technically, at the exact time of the first quarter, a tiny fraction more than half of the Moon is lit, and in the last quarter, a tiny fraction less. The Moon is exactly half-lit when it reaches dichotomy, which occurs several minutes before the first quarter and several minutes after the last quarter.
Moon Rise and Set Times
Below are general guidelines as to where to look for the Moon during each of its phases. Times mentioned are solar time, not clock time. The four primary phases (in italics) rise and set at a point in time; the four secondary phases occur over a broader timespan.
| Phase | Rises Near the East | Highest in the Sky | Sets Near the West |
|---|---|---|---|
| New Moon | Around sunrise | Around noon | Around sunset |
| Waxing Crescent | Between sunrise and noon | Afternoon | Between sunset and midnight |
| First Quarter | Around noon | Around sunset | Around midnight |
| Waxing Gibbous | Between noon and sunset | Evening | Between midnight and sunrise |
| Full Moon | Around sunset | Around midnight | Around sunrise |
| Waning Gibbous | Between sunset and midnight | Early morning | Between sunrise and noon |
| Last Quarter | Around midnight | Around sunrise | Around noon |
| Waning Crescent | Between midnight and sunrise | Morning | Between noon and sunset |